1. Field of the Invention
The present invention relates to insulation of parts for electrical equipment, particularly to electrical insulation of parts for high performance electrical equipment requiring operational reliability at temperatures in excess of that afforded by conventional Class H 220.degree. C. insulation and, more particularly, to electrical insulation in the form of a filament, sheet, wrapper, tape or sleeve which is a flexible composite preform and which is composed entirely of inorganic materials after sintering.
2. Description of the Related Art
Insulation composed of significant quantities of inorganic dielectric materials, such as ceramics including glass and refractories, exhibits poor strength, is not flexible, is difficult to fabricate, and shatters easily. These poor mechanical characteristics have heretofore precluded use of significant quantities of inorganic dielectric materials in electrical insulation for parts for electrical equipment, such as motors. In particular, exclusive use of inorganic dielectric materials for electrical insulation has been limited to only a few specific applications. This is so despite superior properties including uniquely high operating temperatures and advantageous dielectric strength, dielectric constant, and power loss factor, as shown in Table I. Table I compares the properties of various known electrical insulating materials, the data coming from several sources as footnoted.
TABLE I ______________________________________ Electrical Insulating Materials Softening Dielectric Power or Decomposition Constant Factor Temp. .degree.C. ______________________________________ Rubber (Neoprene) 2-3 0.005-0.01 90 Mica/Mica 5-8 1-3 .times. 10.sup.-4 - Compounds Insulating Varnishes 6 0.030 150 Impregnating 3 0.003 40 Compounds (Bitumens & Waxes) Impregnated Fab- 2.5-5.0 0.025-0.10 70 rics glass, with polyester resin Chlorinated Hydro- 3-12 0.063 90 carbons (PVC) Thermosetting Sub- 5-6 0.025 200 stances (phenol aldehyde type) Thermoplastic Resins Polyethylene 2.28 .0003 99-116 Teflon 2.0-2.3 &lt;0.10 400 Paper 1-6 0.02.sup.+ -- Ceramics/Glasses 4-6 6 .times. 10.sup.-4 800-1500 Polymeric Films (polyesters 3.2 0.003 150 fluorocarbons) 2.0 &lt;0.0002 380 Nylon 3.9-7.6 0.08-.1 198-249 ______________________________________ Data from: Clark, F. M., Insulating Materials for Design & Engineering Practice. von Hipple, A. R., Dielectric Materials & Applications. Modern Plastics.